Making one last ditch attempt to revive FrankenMac (my old G4)

I have a MacBook Pro (circa 2008), an old G4 (circa 2001) and a FireWire cable.

Brief history of the G4: I screwed it up big time. When I first switched from OS9 to OSX, I still thought I could go into the folders and move stuff around. (Please don't lecture me. I'm aware of what an idiotic move that was ... NOW.) It's never been right since then. Additionally, the G4 is Frankenmac. It's the better parts of two G4s cobbled together.

The easy solution would seem to be a clean install, but I was scared to attempt that until I had a backup Mac. (Now I do.) I've already backed up the contents of the two HDs, but there are few things on its desktop that I'd like to retrieve before I attempt the clean install.

The primary/startup HD is near death. The MacBook Pro can see it via FireWire, but the G4 won't start up on its own. Can I start the G4 with either my MacBook Pro or its other HD just long enough to grab the files I need?

After that I will remove the offending HD and do a clean install on the remaining one ... if it will let me.

Why bother? I have a Magic Jack that I'd like to use. Obviously I don't want to use it on my laptop. Also, I have a college student who needs a computer for research and typing papers. Also, she just got an iPod for Christmas. I'd like to keep her iTunes separate from mine.

Any words of advice that don't involve me purchasing a new(ish) Mac to replace the G4?

Would it help any if I pinky-swear, cross-my-heart hope-to-die promise to keep my ignorant mitts off the System Folder?